Re: [PATCH] doc: Convert whatisRCU.txt to .rst

[Amol Grover <frextrite@gmail.com>]

On Wed, Nov 06, 2019 at 08:09:50PM +0700, Phong Tran wrote:
> This commit updates whatisRCU.txt to the new .rst format.
> This change includes:
> 
> - Formatting bullet lists
> - Adding literal blocks
> - Links from table of contents to corresponding sections
> - Links to external documents
> - Reformat quick quizzes
> 
> Signed-off-by: Phong Tran <tranmanphong@gmail.com>
> Tested-by: Madhuparna Bhowmik <madhuparnabhowmik04@gmail.com>
> [ tranmanphong: Apply Amol Grover feedback. ]
> Signed-off-by: Paul E. McKenney <paulmck@kernel.org>

Hey Phong,
Tested it, everything is perfect!
Reviewed-by: Amol Grover <frextrite@gmail.com>

Thanks
Amol

> ---
>  Documentation/RCU/index.rst                   |   1 +
>  .../RCU/{whatisRCU.txt => whatisRCU.rst}      | 284 +++++++++++-------
>  2 files changed, 178 insertions(+), 107 deletions(-)
>  rename Documentation/RCU/{whatisRCU.txt => whatisRCU.rst} (84%)
> 
> diff --git a/Documentation/RCU/index.rst b/Documentation/RCU/index.rst
> index 627128c230dc..b9b11481c727 100644
> --- a/Documentation/RCU/index.rst
> +++ b/Documentation/RCU/index.rst
> @@ -8,6 +8,7 @@ RCU concepts
>     :maxdepth: 3
>  
>     arrayRCU
> +   whatisRCU
>     rcu
>     listRCU
>     NMI-RCU
> diff --git a/Documentation/RCU/whatisRCU.txt b/Documentation/RCU/whatisRCU.rst
> similarity index 84%
> rename from Documentation/RCU/whatisRCU.txt
> rename to Documentation/RCU/whatisRCU.rst
> index 58ba05c4d97f..2f6f6ebbc8b0 100644
> --- a/Documentation/RCU/whatisRCU.txt
> +++ b/Documentation/RCU/whatisRCU.rst
> @@ -1,15 +1,18 @@
> +.. _whatisrcu_doc:
> +
>  What is RCU?  --  "Read, Copy, Update"
> +======================================
>  
>  Please note that the "What is RCU?" LWN series is an excellent place
>  to start learning about RCU:
>  
> -1.	What is RCU, Fundamentally?  http://lwn.net/Articles/262464/
> -2.	What is RCU? Part 2: Usage   http://lwn.net/Articles/263130/
> -3.	RCU part 3: the RCU API      http://lwn.net/Articles/264090/
> -4.	The RCU API, 2010 Edition    http://lwn.net/Articles/418853/
> -	2010 Big API Table           http://lwn.net/Articles/419086/
> -5.	The RCU API, 2014 Edition    http://lwn.net/Articles/609904/
> -	2014 Big API Table           http://lwn.net/Articles/609973/
> +| 1.	What is RCU, Fundamentally?  http://lwn.net/Articles/262464/
> +| 2.	What is RCU? Part 2: Usage   http://lwn.net/Articles/263130/
> +| 3.	RCU part 3: the RCU API      http://lwn.net/Articles/264090/
> +| 4.	The RCU API, 2010 Edition    http://lwn.net/Articles/418853/
> +| 	2010 Big API Table           http://lwn.net/Articles/419086/
> +| 5.	The RCU API, 2014 Edition    http://lwn.net/Articles/609904/
> +|	2014 Big API Table           http://lwn.net/Articles/609973/
>  
>  
>  What is RCU?
> @@ -24,14 +27,21 @@ the experience has been that different people must take different paths
>  to arrive at an understanding of RCU.  This document provides several
>  different paths, as follows:
>  
> -1.	RCU OVERVIEW
> -2.	WHAT IS RCU'S CORE API?
> -3.	WHAT ARE SOME EXAMPLE USES OF CORE RCU API?
> -4.	WHAT IF MY UPDATING THREAD CANNOT BLOCK?
> -5.	WHAT ARE SOME SIMPLE IMPLEMENTATIONS OF RCU?
> -6.	ANALOGY WITH READER-WRITER LOCKING
> -7.	FULL LIST OF RCU APIs
> -8.	ANSWERS TO QUICK QUIZZES
> +:ref:`1.	RCU OVERVIEW <1_whatisRCU>`
> +
> +:ref:`2.	WHAT IS RCU'S CORE API? <2_whatisRCU>`
> +
> +:ref:`3.	WHAT ARE SOME EXAMPLE USES OF CORE RCU API? <3_whatisRCU>`
> +
> +:ref:`4.	WHAT IF MY UPDATING THREAD CANNOT BLOCK? <4_whatisRCU>`
> +
> +:ref:`5.	WHAT ARE SOME SIMPLE IMPLEMENTATIONS OF RCU? <5_whatisRCU>`
> +
> +:ref:`6.	ANALOGY WITH READER-WRITER LOCKING <6_whatisRCU>`
> +
> +:ref:`7.	FULL LIST OF RCU APIs <7_whatisRCU>`
> +
> +:ref:`8.	ANSWERS TO QUICK QUIZZES <8_whatisRCU>`
>  
>  People who prefer starting with a conceptual overview should focus on
>  Section 1, though most readers will profit by reading this section at
> @@ -49,8 +59,10 @@ everything, feel free to read the whole thing -- but if you are really
>  that type of person, you have perused the source code and will therefore
>  never need this document anyway.  ;-)
>  
> +.. _1_whatisRCU:
>  
>  1.  RCU OVERVIEW
> +----------------
>  
>  The basic idea behind RCU is to split updates into "removal" and
>  "reclamation" phases.  The removal phase removes references to data items
> @@ -116,8 +128,10 @@ So how the heck can a reclaimer tell when a reader is done, given
>  that readers are not doing any sort of synchronization operations???
>  Read on to learn about how RCU's API makes this easy.
>  
> +.. _2_whatisRCU:
>  
>  2.  WHAT IS RCU'S CORE API?
> +---------------------------
>  
>  The core RCU API is quite small:
>  
> @@ -136,7 +150,7 @@ later.  See the kernel docbook documentation for more info, or look directly
>  at the function header comments.
>  
>  rcu_read_lock()
> -
> +^^^^^^^^^^^^^^^
>  	void rcu_read_lock(void);
>  
>  	Used by a reader to inform the reclaimer that the reader is
> @@ -150,7 +164,7 @@ rcu_read_lock()
>  	longer-term references to data structures.
>  
>  rcu_read_unlock()
> -
> +^^^^^^^^^^^^^^^^^
>  	void rcu_read_unlock(void);
>  
>  	Used by a reader to inform the reclaimer that the reader is
> @@ -158,15 +172,15 @@ rcu_read_unlock()
>  	read-side critical sections may be nested and/or overlapping.
>  
>  synchronize_rcu()
> -
> +^^^^^^^^^^^^^^^^^
>  	void synchronize_rcu(void);
>  
>  	Marks the end of updater code and the beginning of reclaimer
>  	code.  It does this by blocking until all pre-existing RCU
>  	read-side critical sections on all CPUs have completed.
> -	Note that synchronize_rcu() will -not- necessarily wait for
> +	Note that synchronize_rcu() will **not** necessarily wait for
>  	any subsequent RCU read-side critical sections to complete.
> -	For example, consider the following sequence of events:
> +	For example, consider the following sequence of events::
>  
>  	         CPU 0                  CPU 1                 CPU 2
>  	     ----------------- ------------------------- ---------------
> @@ -182,7 +196,7 @@ synchronize_rcu()
>  	any that begin after synchronize_rcu() is invoked.
>  
>  	Of course, synchronize_rcu() does not necessarily return
> -	-immediately- after the last pre-existing RCU read-side critical
> +	**immediately** after the last pre-existing RCU read-side critical
>  	section completes.  For one thing, there might well be scheduling
>  	delays.  For another thing, many RCU implementations process
>  	requests in batches in order to improve efficiencies, which can
> @@ -211,10 +225,10 @@ synchronize_rcu()
>  	checklist.txt for some approaches to limiting the update rate.
>  
>  rcu_assign_pointer()
> -
> +^^^^^^^^^^^^^^^^^^^^
>  	void rcu_assign_pointer(p, typeof(p) v);
>  
> -	Yes, rcu_assign_pointer() -is- implemented as a macro, though it
> +	Yes, rcu_assign_pointer() **is** implemented as a macro, though it
>  	would be cool to be able to declare a function in this manner.
>  	(Compiler experts will no doubt disagree.)
>  
> @@ -231,7 +245,7 @@ rcu_assign_pointer()
>  	the _rcu list-manipulation primitives such as list_add_rcu().
>  
>  rcu_dereference()
> -
> +^^^^^^^^^^^^^^^^^
>  	typeof(p) rcu_dereference(p);
>  
>  	Like rcu_assign_pointer(), rcu_dereference() must be implemented
> @@ -248,13 +262,13 @@ rcu_dereference()
>  
>  	Common coding practice uses rcu_dereference() to copy an
>  	RCU-protected pointer to a local variable, then dereferences
> -	this local variable, for example as follows:
> +	this local variable, for example as follows::
>  
>  		p = rcu_dereference(head.next);
>  		return p->data;
>  
>  	However, in this case, one could just as easily combine these
> -	into one statement:
> +	into one statement::
>  
>  		return rcu_dereference(head.next)->data;
>  
> @@ -266,8 +280,8 @@ rcu_dereference()
>  	unnecessary overhead on Alpha CPUs.
>  
>  	Note that the value returned by rcu_dereference() is valid
> -	only within the enclosing RCU read-side critical section [1].
> -	For example, the following is -not- legal:
> +	only within the enclosing RCU read-side critical section [1]_.
> +	For example, the following is **not** legal::
>  
>  		rcu_read_lock();
>  		p = rcu_dereference(head.next);
> @@ -290,9 +304,9 @@ rcu_dereference()
>  	at any time, including immediately after the rcu_dereference().
>  	And, again like rcu_assign_pointer(), rcu_dereference() is
>  	typically used indirectly, via the _rcu list-manipulation
> -	primitives, such as list_for_each_entry_rcu() [2].
> +	primitives, such as list_for_each_entry_rcu() [2]_.
>  
> -	[1] The variant rcu_dereference_protected() can be used outside
> +.. 	[1] The variant rcu_dereference_protected() can be used outside
>  	of an RCU read-side critical section as long as the usage is
>  	protected by locks acquired by the update-side code.  This variant
>  	avoids the lockdep warning that would happen when using (for
> @@ -305,7 +319,7 @@ rcu_dereference()
>  	a lockdep splat is emitted.  See Documentation/RCU/Design/Requirements/Requirements.rst
>  	and the API's code comments for more details and example usage.
>  
> -	[2] If the list_for_each_entry_rcu() instance might be used by
> +.. 	[2] If the list_for_each_entry_rcu() instance might be used by
>  	update-side code as well as by RCU readers, then an additional
>  	lockdep expression can be added to its list of arguments.
>  	For example, given an additional "lock_is_held(&mylock)" argument,
> @@ -315,6 +329,7 @@ rcu_dereference()
>  
>  The following diagram shows how each API communicates among the
>  reader, updater, and reclaimer.
> +::
>  
>  
>  	    rcu_assign_pointer()
> @@ -375,12 +390,16 @@ c.	RCU applied to scheduler and interrupt/NMI-handler tasks.
>  Again, most uses will be of (a).  The (b) and (c) cases are important
>  for specialized uses, but are relatively uncommon.
>  
> +.. _3_whatisRCU:
>  
>  3.  WHAT ARE SOME EXAMPLE USES OF CORE RCU API?
> +-----------------------------------------------
>  
>  This section shows a simple use of the core RCU API to protect a
>  global pointer to a dynamically allocated structure.  More-typical
> -uses of RCU may be found in listRCU.txt, arrayRCU.txt, and NMI-RCU.txt.
> +uses of RCU may be found in :ref:`listRCU.rst <list_rcu_doc>`,
> +:ref:`arrayRCU.rst <array_rcu_doc>`, and :ref:`NMI-RCU.rst <NMI_rcu_doc>`.
> +::
>  
>  	struct foo {
>  		int a;
> @@ -440,40 +459,43 @@ uses of RCU may be found in listRCU.txt, arrayRCU.txt, and NMI-RCU.txt.
>  
>  So, to sum up:
>  
> -o	Use rcu_read_lock() and rcu_read_unlock() to guard RCU
> +-	Use rcu_read_lock() and rcu_read_unlock() to guard RCU
>  	read-side critical sections.
>  
> -o	Within an RCU read-side critical section, use rcu_dereference()
> +-	Within an RCU read-side critical section, use rcu_dereference()
>  	to dereference RCU-protected pointers.
>  
> -o	Use some solid scheme (such as locks or semaphores) to
> +-	Use some solid scheme (such as locks or semaphores) to
>  	keep concurrent updates from interfering with each other.
>  
> -o	Use rcu_assign_pointer() to update an RCU-protected pointer.
> +-	Use rcu_assign_pointer() to update an RCU-protected pointer.
>  	This primitive protects concurrent readers from the updater,
> -	-not- concurrent updates from each other!  You therefore still
> +	**not** concurrent updates from each other!  You therefore still
>  	need to use locking (or something similar) to keep concurrent
>  	rcu_assign_pointer() primitives from interfering with each other.
>  
> -o	Use synchronize_rcu() -after- removing a data element from an
> -	RCU-protected data structure, but -before- reclaiming/freeing
> +-	Use synchronize_rcu() **after** removing a data element from an
> +	RCU-protected data structure, but **before** reclaiming/freeing
>  	the data element, in order to wait for the completion of all
>  	RCU read-side critical sections that might be referencing that
>  	data item.
>  
>  See checklist.txt for additional rules to follow when using RCU.
> -And again, more-typical uses of RCU may be found in listRCU.txt,
> -arrayRCU.txt, and NMI-RCU.txt.
> +And again, more-typical uses of RCU may be found in :ref:`listRCU.rst
> +<list_rcu_doc>`, :ref:`arrayRCU.rst <array_rcu_doc>`, and :ref:`NMI-RCU.rst
> +<NMI_rcu_doc>`.
>  
> +.. _4_whatisRCU:
>  
>  4.  WHAT IF MY UPDATING THREAD CANNOT BLOCK?
> +--------------------------------------------
>  
>  In the example above, foo_update_a() blocks until a grace period elapses.
>  This is quite simple, but in some cases one cannot afford to wait so
>  long -- there might be other high-priority work to be done.
>  
>  In such cases, one uses call_rcu() rather than synchronize_rcu().
> -The call_rcu() API is as follows:
> +The call_rcu() API is as follows::
>  
>  	void call_rcu(struct rcu_head * head,
>  		      void (*func)(struct rcu_head *head));
> @@ -481,7 +503,7 @@ The call_rcu() API is as follows:
>  This function invokes func(head) after a grace period has elapsed.
>  This invocation might happen from either softirq or process context,
>  so the function is not permitted to block.  The foo struct needs to
> -have an rcu_head structure added, perhaps as follows:
> +have an rcu_head structure added, perhaps as follows::
>  
>  	struct foo {
>  		int a;
> @@ -490,7 +512,7 @@ have an rcu_head structure added, perhaps as follows:
>  		struct rcu_head rcu;
>  	};
>  
> -The foo_update_a() function might then be written as follows:
> +The foo_update_a() function might then be written as follows::
>  
>  	/*
>  	 * Create a new struct foo that is the same as the one currently
> @@ -520,7 +542,7 @@ The foo_update_a() function might then be written as follows:
>  		call_rcu(&old_fp->rcu, foo_reclaim);
>  	}
>  
> -The foo_reclaim() function might appear as follows:
> +The foo_reclaim() function might appear as follows::
>  
>  	void foo_reclaim(struct rcu_head *rp)
>  	{
> @@ -544,7 +566,7 @@ namely foo_reclaim().
>  The summary of advice is the same as for the previous section, except
>  that we are now using call_rcu() rather than synchronize_rcu():
>  
> -o	Use call_rcu() -after- removing a data element from an
> +-	Use call_rcu() **after** removing a data element from an
>  	RCU-protected data structure in order to register a callback
>  	function that will be invoked after the completion of all RCU
>  	read-side critical sections that might be referencing that
> @@ -552,14 +574,16 @@ o	Use call_rcu() -after- removing a data element from an
>  
>  If the callback for call_rcu() is not doing anything more than calling
>  kfree() on the structure, you can use kfree_rcu() instead of call_rcu()
> -to avoid having to write your own callback:
> +to avoid having to write your own callback::
>  
>  	kfree_rcu(old_fp, rcu);
>  
>  Again, see checklist.txt for additional rules governing the use of RCU.
>  
> +.. _5_whatisRCU:
>  
>  5.  WHAT ARE SOME SIMPLE IMPLEMENTATIONS OF RCU?
> +------------------------------------------------
>  
>  One of the nice things about RCU is that it has extremely simple "toy"
>  implementations that are a good first step towards understanding the
> @@ -579,7 +603,7 @@ more details on the current implementation as of early 2004.
>  
>  
>  5A.  "TOY" IMPLEMENTATION #1: LOCKING
> -
> +^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
>  This section presents a "toy" RCU implementation that is based on
>  familiar locking primitives.  Its overhead makes it a non-starter for
>  real-life use, as does its lack of scalability.  It is also unsuitable
> @@ -591,7 +615,7 @@ you allow nested rcu_read_lock() calls, you can deadlock.
>  However, it is probably the easiest implementation to relate to, so is
>  a good starting point.
>  
> -It is extremely simple:
> +It is extremely simple::
>  
>  	static DEFINE_RWLOCK(rcu_gp_mutex);
>  
> @@ -614,7 +638,7 @@ It is extremely simple:
>  
>  [You can ignore rcu_assign_pointer() and rcu_dereference() without missing
>  much.  But here are simplified versions anyway.  And whatever you do,
> -don't forget about them when submitting patches making use of RCU!]
> +don't forget about them when submitting patches making use of RCU!]::
>  
>  	#define rcu_assign_pointer(p, v) \
>  	({ \
> @@ -647,18 +671,23 @@ that the only thing that can block rcu_read_lock() is a synchronize_rcu().
>  But synchronize_rcu() does not acquire any locks while holding rcu_gp_mutex,
>  so there can be no deadlock cycle.
>  
> -Quick Quiz #1:	Why is this argument naive?  How could a deadlock
> +.. _quiz_1:
> +
> +Quick Quiz #1:
> +		Why is this argument naive?  How could a deadlock
>  		occur when using this algorithm in a real-world Linux
>  		kernel?  How could this deadlock be avoided?
>  
> +:ref:`Answers to Quick Quiz <8_whatisRCU>`
>  
>  5B.  "TOY" EXAMPLE #2: CLASSIC RCU
> -
> +^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
>  This section presents a "toy" RCU implementation that is based on
>  "classic RCU".  It is also short on performance (but only for updates) and
>  on features such as hotplug CPU and the ability to run in CONFIG_PREEMPT
>  kernels.  The definitions of rcu_dereference() and rcu_assign_pointer()
>  are the same as those shown in the preceding section, so they are omitted.
> +::
>  
>  	void rcu_read_lock(void) { }
>  
> @@ -683,14 +712,14 @@ CPU in turn.  The run_on() primitive can be implemented straightforwardly
>  in terms of the sched_setaffinity() primitive.  Of course, a somewhat less
>  "toy" implementation would restore the affinity upon completion rather
>  than just leaving all tasks running on the last CPU, but when I said
> -"toy", I meant -toy-!
> +"toy", I meant **toy**!
>  
>  So how the heck is this supposed to work???
>  
>  Remember that it is illegal to block while in an RCU read-side critical
>  section.  Therefore, if a given CPU executes a context switch, we know
>  that it must have completed all preceding RCU read-side critical sections.
> -Once -all- CPUs have executed a context switch, then -all- preceding
> +Once **all** CPUs have executed a context switch, then **all** preceding
>  RCU read-side critical sections will have completed.
>  
>  So, suppose that we remove a data item from its structure and then invoke
> @@ -698,19 +727,32 @@ synchronize_rcu().  Once synchronize_rcu() returns, we are guaranteed
>  that there are no RCU read-side critical sections holding a reference
>  to that data item, so we can safely reclaim it.
>  
> -Quick Quiz #2:	Give an example where Classic RCU's read-side
> -		overhead is -negative-.
> +.. _quiz_2:
> +
> +Quick Quiz #2:
> +		Give an example where Classic RCU's read-side
> +		overhead is **negative**.
> +
> +:ref:`Answers to Quick Quiz <8_whatisRCU>`
>  
> -Quick Quiz #3:  If it is illegal to block in an RCU read-side
> +.. _quiz_3:
> +
> +Quick Quiz #3:
> +		If it is illegal to block in an RCU read-side
>  		critical section, what the heck do you do in
>  		PREEMPT_RT, where normal spinlocks can block???
>  
> +:ref:`Answers to Quick Quiz <8_whatisRCU>`
> +
> +.. _6_whatisRCU:
>  
>  6.  ANALOGY WITH READER-WRITER LOCKING
> +--------------------------------------
>  
>  Although RCU can be used in many different ways, a very common use of
>  RCU is analogous to reader-writer locking.  The following unified
>  diff shows how closely related RCU and reader-writer locking can be.
> +::
>  
>  	@@ -5,5 +5,5 @@ struct el {
>  	 	int data;
> @@ -762,7 +804,7 @@ diff shows how closely related RCU and reader-writer locking can be.
>  		return 0;
>  	 }
>  
> -Or, for those who prefer a side-by-side listing:
> +Or, for those who prefer a side-by-side listing::
>  
>   1 struct el {                          1 struct el {
>   2   struct list_head list;             2   struct list_head list;
> @@ -774,40 +816,44 @@ Or, for those who prefer a side-by-side listing:
>   8 rwlock_t listmutex;                  8 spinlock_t listmutex;
>   9 struct el head;                      9 struct el head;
>  
> - 1 int search(long key, int *result)    1 int search(long key, int *result)
> - 2 {                                    2 {
> - 3   struct list_head *lp;              3   struct list_head *lp;
> - 4   struct el *p;                      4   struct el *p;
> - 5                                      5
> - 6   read_lock(&listmutex);             6   rcu_read_lock();
> - 7   list_for_each_entry(p, head, lp) { 7   list_for_each_entry_rcu(p, head, lp) {
> - 8     if (p->key == key) {             8     if (p->key == key) {
> - 9       *result = p->data;             9       *result = p->data;
> -10       read_unlock(&listmutex);      10       rcu_read_unlock();
> -11       return 1;                     11       return 1;
> -12     }                               12     }
> -13   }                                 13   }
> -14   read_unlock(&listmutex);          14   rcu_read_unlock();
> -15   return 0;                         15   return 0;
> -16 }                                   16 }
> -
> - 1 int delete(long key)                 1 int delete(long key)
> - 2 {                                    2 {
> - 3   struct el *p;                      3   struct el *p;
> - 4                                      4
> - 5   write_lock(&listmutex);            5   spin_lock(&listmutex);
> - 6   list_for_each_entry(p, head, lp) { 6   list_for_each_entry(p, head, lp) {
> - 7     if (p->key == key) {             7     if (p->key == key) {
> - 8       list_del(&p->list);            8       list_del_rcu(&p->list);
> - 9       write_unlock(&listmutex);      9       spin_unlock(&listmutex);
> -                                       10       synchronize_rcu();
> -10       kfree(p);                     11       kfree(p);
> -11       return 1;                     12       return 1;
> -12     }                               13     }
> -13   }                                 14   }
> -14   write_unlock(&listmutex);         15   spin_unlock(&listmutex);
> -15   return 0;                         16   return 0;
> -16 }                                   17 }
> +::
> +
> +  1 int search(long key, int *result)    1 int search(long key, int *result)
> +  2 {                                    2 {
> +  3   struct list_head *lp;              3   struct list_head *lp;
> +  4   struct el *p;                      4   struct el *p;
> +  5                                      5
> +  6   read_lock(&listmutex);             6   rcu_read_lock();
> +  7   list_for_each_entry(p, head, lp) { 7   list_for_each_entry_rcu(p, head, lp) {
> +  8     if (p->key == key) {             8     if (p->key == key) {
> +  9       *result = p->data;             9       *result = p->data;
> + 10       read_unlock(&listmutex);      10       rcu_read_unlock();
> + 11       return 1;                     11       return 1;
> + 12     }                               12     }
> + 13   }                                 13   }
> + 14   read_unlock(&listmutex);          14   rcu_read_unlock();
> + 15   return 0;                         15   return 0;
> + 16 }                                   16 }
> +
> +::
> +
> +  1 int delete(long key)                 1 int delete(long key)
> +  2 {                                    2 {
> +  3   struct el *p;                      3   struct el *p;
> +  4                                      4
> +  5   write_lock(&listmutex);            5   spin_lock(&listmutex);
> +  6   list_for_each_entry(p, head, lp) { 6   list_for_each_entry(p, head, lp) {
> +  7     if (p->key == key) {             7     if (p->key == key) {
> +  8       list_del(&p->list);            8       list_del_rcu(&p->list);
> +  9       write_unlock(&listmutex);      9       spin_unlock(&listmutex);
> +                                        10       synchronize_rcu();
> + 10       kfree(p);                     11       kfree(p);
> + 11       return 1;                     12       return 1;
> + 12     }                               13     }
> + 13   }                                 14   }
> + 14   write_unlock(&listmutex);         15   spin_unlock(&listmutex);
> + 15   return 0;                         16   return 0;
> + 16 }                                   17 }
>  
>  Either way, the differences are quite small.  Read-side locking moves
>  to rcu_read_lock() and rcu_read_unlock, update-side locking moves from
> @@ -825,15 +871,17 @@ delete() can now block.  If this is a problem, there is a callback-based
>  mechanism that never blocks, namely call_rcu() or kfree_rcu(), that can
>  be used in place of synchronize_rcu().
>  
> +.. _7_whatisRCU:
>  
>  7.  FULL LIST OF RCU APIs
> +-------------------------
>  
>  The RCU APIs are documented in docbook-format header comments in the
>  Linux-kernel source code, but it helps to have a full list of the
>  APIs, since there does not appear to be a way to categorize them
>  in docbook.  Here is the list, by category.
>  
> -RCU list traversal:
> +RCU list traversal::
>  
>  	list_entry_rcu
>  	list_first_entry_rcu
> @@ -854,7 +902,7 @@ RCU list traversal:
>  	hlist_bl_first_rcu
>  	hlist_bl_for_each_entry_rcu
>  
> -RCU pointer/list update:
> +RCU pointer/list udate::
>  
>  	rcu_assign_pointer
>  	list_add_rcu
> @@ -876,7 +924,9 @@ RCU pointer/list update:
>  	hlist_bl_del_rcu
>  	hlist_bl_set_first_rcu
>  
> -RCU:	Critical sections	Grace period		Barrier
> +RCU::
> +
> +	Critical sections	Grace period		Barrier
>  
>  	rcu_read_lock		synchronize_net		rcu_barrier
>  	rcu_read_unlock		synchronize_rcu
> @@ -885,7 +935,9 @@ RCU:	Critical sections	Grace period		Barrier
>  	rcu_dereference_check	kfree_rcu
>  	rcu_dereference_protected
>  
> -bh:	Critical sections	Grace period		Barrier
> +bh::
> +
> +	Critical sections	Grace period		Barrier
>  
>  	rcu_read_lock_bh	call_rcu		rcu_barrier
>  	rcu_read_unlock_bh	synchronize_rcu
> @@ -896,7 +948,9 @@ bh:	Critical sections	Grace period		Barrier
>  	rcu_dereference_bh_protected
>  	rcu_read_lock_bh_held
>  
> -sched:	Critical sections	Grace period		Barrier
> +sched::
> +
> +	Critical sections	Grace period		Barrier
>  
>  	rcu_read_lock_sched	call_rcu		rcu_barrier
>  	rcu_read_unlock_sched	synchronize_rcu
> @@ -910,7 +964,9 @@ sched:	Critical sections	Grace period		Barrier
>  	rcu_read_lock_sched_held
>  
>  
> -SRCU:	Critical sections	Grace period		Barrier
> +SRCU::
> +
> +	Critical sections	Grace period		Barrier
>  
>  	srcu_read_lock		call_srcu		srcu_barrier
>  	srcu_read_unlock	synchronize_srcu
> @@ -918,13 +974,14 @@ SRCU:	Critical sections	Grace period		Barrier
>  	srcu_dereference_check
>  	srcu_read_lock_held
>  
> -SRCU:	Initialization/cleanup
> +SRCU: Initialization/cleanup::
> +
>  	DEFINE_SRCU
>  	DEFINE_STATIC_SRCU
>  	init_srcu_struct
>  	cleanup_srcu_struct
>  
> -All:  lockdep-checked RCU-protected pointer access
> +All: lockdep-checked RCU-protected pointer access::
>  
>  	rcu_access_pointer
>  	rcu_dereference_raw
> @@ -974,15 +1031,19 @@ g.	Otherwise, use RCU.
>  Of course, this all assumes that you have determined that RCU is in fact
>  the right tool for your job.
>  
> +.. _8_whatisRCU:
>  
>  8.  ANSWERS TO QUICK QUIZZES
> +----------------------------
>  
> -Quick Quiz #1:	Why is this argument naive?  How could a deadlock
> +Quick Quiz #1:
> +		Why is this argument naive?  How could a deadlock
>  		occur when using this algorithm in a real-world Linux
>  		kernel?  [Referring to the lock-based "toy" RCU
>  		algorithm.]
>  
> -Answer:		Consider the following sequence of events:
> +Answer:
> +		Consider the following sequence of events:
>  
>  		1.	CPU 0 acquires some unrelated lock, call it
>  			"problematic_lock", disabling irq via
> @@ -1021,10 +1082,14 @@ Answer:		Consider the following sequence of events:
>  		approach where tasks in RCU read-side critical sections
>  		cannot be blocked by tasks executing synchronize_rcu().
>  
> -Quick Quiz #2:	Give an example where Classic RCU's read-side
> -		overhead is -negative-.
> +:ref:`Back to Quick Quiz #1 <quiz_1>`
> +
> +Quick Quiz #2:
> +		Give an example where Classic RCU's read-side
> +		overhead is **negative**.
>  
> -Answer:		Imagine a single-CPU system with a non-CONFIG_PREEMPT
> +Answer:
> +		Imagine a single-CPU system with a non-CONFIG_PREEMPT
>  		kernel where a routing table is used by process-context
>  		code, but can be updated by irq-context code (for example,
>  		by an "ICMP REDIRECT" packet).	The usual way of handling
> @@ -1046,11 +1111,15 @@ Answer:		Imagine a single-CPU system with a non-CONFIG_PREEMPT
>  		even the theoretical possibility of negative overhead for
>  		a synchronization primitive is a bit unexpected.  ;-)
>  
> -Quick Quiz #3:  If it is illegal to block in an RCU read-side
> +:ref:`Back to Quick Quiz #2 <quiz_2>`
> +
> +Quick Quiz #3:
> +		If it is illegal to block in an RCU read-side
>  		critical section, what the heck do you do in
>  		PREEMPT_RT, where normal spinlocks can block???
>  
> -Answer:		Just as PREEMPT_RT permits preemption of spinlock
> +Answer:
> +		Just as PREEMPT_RT permits preemption of spinlock
>  		critical sections, it permits preemption of RCU
>  		read-side critical sections.  It also permits
>  		spinlocks blocking while in RCU read-side critical
> @@ -1069,6 +1138,7 @@ Answer:		Just as PREEMPT_RT permits preemption of spinlock
>  		Besides, how does the computer know what pizza parlor
>  		the human being went to???
>  
> +:ref:`Back to Quick Quiz #3 <quiz_3>`
>  
>  ACKNOWLEDGEMENTS
>  
> -- 
> 2.20.1
>